Process for preparing a platinum metalcrystalline zeolite catalyst



United States Patent O 3 226,339 PROQESS FOR PREPAitlNG A PLATINUMMETAL- QRYSTALLHNE ZEQLITE CATALYST Vincent .l'. Friiette, Briton, Ni,and Russell W. Maatman, Oxford, Miss, assignors to Socony Mobil OilCompany, Inc, a corporation of New York No Drawing. Filed Nov. 17, 1958,Ser. No. 774,143 if) Claims. (Cl. Z52455) This invention relates to anew and useful platinum metal-containing catalyst. More particularly,the present invention is directed to a catalytic composition consistingessentially of activated platinum metal distributed within the pores ofa crystalline inorganic zeolite characterized by rigid three dimensionalnetworks and uniform interstitial dimensions sufficiently large topermit introduction by ion exchange of a platinum metal-containing ion.The invention is further directed to a method for preparing suchcatalytic compositions.

Catalysts containing metals of the platinum series, i.e. metals ofatomic numbers 44 to 46 and 76 to 78 inclusive, have become ofconsiderable commercial significance in recent years. Thus, such metalsimpregnated on alumina and silica-alumina supports are widely employedin reforming operations to produce gasolines of high octane number. Ingeneral, supported platinum metal catalysts are capable of catalyticallyeffecting a variety of complex hydrocarbon conversion reactions. Forexample, it is known that during reforming paraffin hydrocarbons undergoisomerization, naphthenes are dehydrogenated to aromatics and olefinsare hydrogenated to paraffins. In each of these component reactions,however, there is, in so far as known no marked selectivity for anyparticular reactant or group of reactants.

The catalyst of the present invention affords a platinummetal-containing catalytic composition having the ability to operateselectively on certain members of one or more different reactantsundergoing catalytic conversion. The selectivity attained with the newcatalysts described herein is believed attributable to the solid,crystalline, zeolitic structure of the support characterized by rigidthree dimensional networks and uniform interstitial dimensions in whichthe platinum metal component is dispersed. By associating the platinummetal in highly dispersed form with the intra-crystalline spaces for thechemical reaction system which is to be catalyzed thereby, only suchconversion paths are obtained which involve reactant or productmolecules of such specific shapes or sizes. Such zeolites wherein onlymolecules of particular size and shape are able to enter are sometimesknown as molecular sieves.

In one embodiment, the present invention provides a catalyst consistingessentially of a platinum metal dispersed within the pores of acrystalline zeolitic structure characterized by rigid three dimensionalnetworks and uniform pores sufficiently large to at least admitcyclohexane, and particularly to 13 Angstrom units in diameter.

Another embodiment of the invention resides in a method of catalystpreparation wherein a crystalline aluminosilicate zeolite, initiallyfree of platinum metal, and having rigid three dimensional networkscharacterized by uniform interstitial dimensions, sufliciently large topermit introduction by ion exchange of a platinum metal-containing ion,is brought into contact with a solution of an ionizable platinum metalcompound for a sufficient period of time to effect deposition on thecrystalline structure of the zeolite of a platinum metal-containing ionand subsequently dried and thereafter activated by thermal treatment ata temperature in the approximate range of 250 F. to 1100 F. to effect atleast partial conversion of the platinum metal-containing ion to acatalytically active state.

A further embodiment of the invention affords a meth- 0d of catalystpreparation in which a crystalline aluminosilicate zeolite, initiallyfree of platinum metal, and having rigid three dimensional networkscharacterized by uniform interstitial dimensions sufficiently large topermit introduction by ion exchange of a platinum metalcontaining ion,is contacted with a solution of an ionizable platinum metal compound andan ionizable nonplatium metal compound whereby a uniform distribution ofplatinum metal on the zeolite is achieved, followed by drying andactivation of the resulting composite upon thermal treatment at atemperature in the approximate range of 250 F. to 1100 F.

A still further embodiment of the present invention involves a methodfor preparation of a platinum metalcontaining catalyst by contacting acrystalline non-platinum metal aluminosilicate zeolite having rigidthree dimensional networks characterized by uniform interstitialdimensions, sufficiently large to permit introduction by ion exchange ofa platinum metal-containing ion with a solution of an ionizable platinummetal compound for a sufficient time to effect deposition on thecrystalline zeolite structure of a platinum metal-containing ion,followed by drying the resulting composite and activating the same byheating in an atmosphere containing free oxygen at a temperature withinthe approximate range of 250 F. to ll0O F. for A hour to 24 hours andthereafter in an atmosphere of hydrogen at a temperature within theabove range to effect at least partial reduction of the platinummetal-containing ion to platinum metal.

In yet another embodiment of the invention, a catalyst is produced byexchanging a substantial proportion of the original metal ion containedin a crystalline aluminosilicate, initially free of platinum metal andhaving a structure of rigid three dimensional networks characterized byuniform pores approximately 10 to 13 Angstroms in diameter with anionizable platinum metal compound, n which the platinum metal is in thecationic state, drying the resulting composite and activating the sameby thermal treatment at a temperature in the approximate range of 250 F.to 1100 F. to effect at least partial conversion of the platinummetal-containing cation to a catalytically active state.

The crystalline aluminosilicate zeolites employed in preparation of theplatinum metal catalyst described herein are adsorbents designated asmolecular sieves. Such materials have heretofore been utilized foreffecting physical separation of mixtures of materials of varyingmolecular size. Such substances have been described by Barrer in severalpublications and in US 2,306,610 and US. 2,413,134. Thus, molecularsieves are essentially the dehydrated forms of crystalline natural orsynthetic hydrous siliceous zeolites containing varying quantities ofsodium, calcium, and aluminum with or without other metals. All or aportion of the sodium or calcium ions normally contained in themolecular sieves structure may be zeolitically replaced with a number ofvarious other ions. The atoms of sodium, calcium or metals inreplacement thereof, silicon, aluminum and oxygen in these zeolites arearranged, in the form of an aluminosilicate salt in a definite andconsistent crystalline pattern. This structure contains a large numberof small cavities, interconnected by a number of still smaller holes orchannels. These cavities and channels are precisely uniform in size.Chemically, these zeolites may be represented by the general formula:

where Me is a metal cation, x/n is the number of exchangeable cations ofvalence n, x is also the number of aluminum atoms combined in the formof aluminate, y is the number of silicon atoms and z is the number ofwater molecules, removal of which produces the characteristic channelsystem. In the above formula, the ratio y/x is a number from 1 to 5 andusually 1 to 2. At the present time, there are commercially availablemolecular sieves f the A series, and of the X series. A syntheticzeolite known as Molecular Sieve 4A is a crystalline sodiumaluminosilicate having channels about 4 Angstroms in diameter. In thehydrated form, this material is chemically characterized by the formula:

The synthetic zeolite known as Molecular Sieve 5A is a crystallinealuminosilicate salt having channels about 5 Angstroms in diameter andin which substantially all of the 12 ions of sodium in the immediatelyabove formula are replaced by calcium, it being understood that calciumreplaces sodium in the ratio of one calcium ion for two sodium ions. Acrystalline sodium aluminosilicate which has pores or channels ofapproximately 13 Angstrom units in diameter is also availablecommercially under the name of Molecular Sieve 13X. The letter X is usedto distinguish the inter-atomic structure of this zeolite from that ofthe A crystal mentioned above. As prepared, the 13X material containswater and has the unit C611 formula Na [(A1O (SiO) The material isstructurally identical with faujasite, a naturally occurring zeolite.Faujasite, however, is not identical in composition with the 13Xzeolite. The synthetic zeolite known as Molecular Sieve X is acrystalline aluminosilicate salt having channels about 10 Angstrom unitsin diameter and in which a substantial proportion of the sodium ions ofthe 13X material have been replaced by calcium.

Molecular sieves of the A series consist fundamentally of a tetrahedralthree dimensional structure of silicon and aluminum. These tetrahedraare joined by sharing oxygen atoms in such a manner that the ratio ofatoms of oxygen to the total number of atoms of aluminum and silicon isequal to two. The electrovalence of the tetrahe-dra containing aluminumis balanced by the inclusion in the crystal of a cation, for example, analkali metal or an alkaline earth metal cation. This equilibrium can beexpressed by the formula wherein the ratio of A1 to the number of thecations such as Ca, Sr, N21 K or Li is equal to unity. One cation may beexchanged either in entirety or partially by another cation utilizingion exchange techniques. The spaces between the tetrahedra are occupiedby molecules of water prior to dehydration.

Molecular sieves of the A series are ordinarily prepared initially inthe sodium form of the crystal. The sodium ions in such form may, asdesired, be exchanged for other cations. In general, the process ofpreparation involves heating, in aqueous solution, an appropriatemixture of oxides, or of materials whose chemical composition can becompletely represented as a mixture of oxides Na O, Al O ,SiO and H 0 ata temperature of approximately 100 C. for periods of 15 minutes to hoursor more. The product, which crystallize-s within this hot mixture isseparated therefrom and water-washed until the Water in equilibrium withthe zeolite has a pH in the range of 9 to 12 and thereafter dehydratedby heating.

The empirical formula for the zeolites utilized herein as an initialreactant can be expressed as:

Mg/ o A1203 where M is a metal other than those of the platinum seriesand it its valence. A specific crystalline zeolite has values of X and Ywithin a definite range. The value of X for any specific zeolite variesin a certain manner depending on whether aluminum or silicon atomsoccupy equivalent positions in the lattice. For molecular sieves of theA series, X has an average value of 1.85i0.5. The value of Y, dependingon the condition of hydration and on the metal cation present may varyfrom 6 to 0. The average value of Y for the completely hydrated sodiumzeolite of the A series is 5.1. In the above general formula, the ratioof Na O to A1 0 is equal to 1. However, if during the process ofpreparation, excess of the base present in the mother liquor is noteliminated by washing of the crystalline precipitate, analysis will showa ratio slightly greater than 1. On the other hand, if the washing isexcessive a certain amount of exchange of the sodium with hydrogen ionsmay take place bringing the aforementioned ratio to slightly lessthan 1. The ratio M O to A1 0 in the above general formula mayaccordingly be defined more accurately as being 1:0.2.

Suitable reagents in the preparation of the sodium zeolite of the Aseries include silica gel, silicic acid, or sodium silicate as sourcesof silica. Alumina can be supplied by utilizing activated alumina, gammaalumina, alpha alumina, aluminum trihydrate or sodium aluminate. Sodiumhydroxide is suitably used as the source of the sodium ion and inaddition contributes to the regulation of the pH. All reagents arepreferably soluble in water. The reaction solution has a composition,expressed as mixtures of oxides, within the following ranges SiO /A1 Oof 0.5 to 2.5, Na O/SiO of 0.8 to 3.0 and H O/Na O of 35 to 200. Thereaction mixture is placed in a suitable vessel which is closed to theatmosphere in order to avoid losses of water and the reagents are thenheated for an appropriate length of time. A convenient and generallyemployed process of preparation involves preparing an aqueous solutionof sodium aluminate and sodium hydroxide and then adding with stirringan aqueous solution of sodium silicate. While satisfactorycrystallization may be obtained at temperatures from 21 C. to 150 C.,the pressure being atmospheric or less, corresponding to the equilibriumof the vapor pressure with the mixture at the reaction temperature,crystallization is ordinarily carried out t about C. For temperaturesbetween room temperature (21 C.) and C. an increase in temperatureincreases the velocity of the reaction and thus decreases its duration.As soon as the zeolite crystals are completely formed they retain theirstructure and it is not essential to maintain the temperature of thereaction any longer in order to obtain a maximum yield of crystals.

After formation, the crystalline zeolite is separated from the motherliquor, usually by filtration. The crystalline mass is then washedpreferably with distilled water, and while on the filter, until the washWater, in equilibrium with the zeolite, reaches a pH of 9 to 12. Thecrystals are then dried at a temperature between 25 C. and 150 C.

As indicated hereinabove, the sodium ions of the above zeolite may bereplaced partially or completely by other cations. These replacing ionsinclude other monovalent or divalent cations such as lithium andmagnesium, metal ions of the first group of the Periodic Table such aspotassium and silver, metal ions of the second group such as calcium andstrontium, and other ions including cobalt and ammonium which, with thesodium zeolite of the A series, react as metal in that they replacesodium ions without occassioning any appreciable change in thefundamental structure of the crystalline zeolite. Replacement issuitably accomplished by contacting the crystalline sodiumaluminosilicate zeolite with a solution of an ionizable compound of theion which is to be zeolitically introduced into the molecular sievestructure for a sufficient time to bring about the extent of desiredintroduction of such ion. After such treatment, the resulting exchangedproduct is Water-washed and dried. The extent to which exchange takesplace can be controlled. Thus, taking the exchange of sodium for calciumas a typical example, such exchange can be effected in a proportion ofless than 5 percent up to 100 percent by contacting a known amount ofthe sodium zeolite with solutions containing determined amounts ofexchangeable ions.

Sodium zeolite of the A series exchanged with calcium or magnesiumpossesses larger pores than the unexchanged material. An unusualcharacteristic of the calcium or magnesium exchanged zeolites is thatthe opening of the pores is not accomplished progressively as the sodiumions are replaced by calcium ions but is produced within a fairly narrowrange of composition. When the exchange is 25 percent or less, thesubstance possesses substantially the same pore characteristics as thesodium zeolite of the A series, namely a pore diameter of about 4Angstrom units. However, when the exchange exceeds 40 percent, the porecharacteristics become those of the calcium and magnesium zeolites ofthe A series, i.e. a pore diameter of about 5 Angstrom units. Thisremarkable affect is evident, for example, by the amount of normalheptane adsorbed on the sodium zeolite of the A series with increasingreplacement of the sodium ions therein with calcium as shown below:

Percent of Sodium Ions Replaced in Molecular Sieve 4A by Calcium IonsWt. Percent of Normal Heptane Adsorbed at 25 C. Under 45 mm. of MercuryAs noted hereinabove, there are numerous forms of zeolites of the Aseries having exchanged ions. While, generally, the substances having adivalent exchanged ion such as magnesium and strontium zeolites, havepore size characteristics analogous to those of calcium of the A series,the exact pore size will differ. Such property can be advantageouslyemployed in affording control of pore size of suitable selection of aparticular cation. Similarly, the substances having a monovalent ionsuch as lithium and silver zeolites of the A series have pore sizecharacteristics similar to the sodium zeolite of such series, but theprecise pore size is subject to similar control and selection.

Molecular sieves of the X series are characterized by the formula:

where M is Na+ or Ca++ or other ions of the type mentioned hereinabov-eintroduced by replacement thereof and n represents the valence of thecation M. The structure consists of a complex assembly of 192 tetrahedrain a large cubic unit cell 24.95 A. on an edge. The effective porediameter is 10 to 13 A. and the adsorption volume is about 0.35 oc./gram of dehydrated zeolite.

For molecular sieves of this series, in the empirical formula:

M2/ OAi203 X has an average value of 2.5i0.5. The value of Y, dependingon the condition of hydration and on the metal cation present may varyfrom 8 to 0. The average value of Y for the completely hydrated sodiumzeolite of the X series is 6.2.

Molecular sieves of the X series are prepared in a manner similar tothat described hereinabove for preparation of molecular sieves of the Aseries. However, for synthesis of the X series molecular sieves, thereaction mixture has a composition, expressed as mixtures of oxides,within the following limits: SiO /Al O of 3 to 5, Na O/SiO of 1.2 to 1.5and H O/NaO of 35 to 60.

The catalysts of the present invention are prepared by bringing asuitable crystalline zeolite of the nature described above and havinguniform interstitial dimensions, sufiiciently large to permitintroduction by ion exchange of a platinum metal-containing ion, intocontact with an ionizable compound of a platinum metal for a sufiicientperiod of time to effect deposition on the crystalline structure of thezeolite of a platinum metal-containing ion derived from such solution,drying the resulting composite and subjecting the same to an activatingtreatment.

The platinum metals, i.e. metals of the platinum series contained in thepresent catalyst composition include those having atomic numbers 44 to46 and 76 to 78 inclusive, namely platinum, palladium, ruthenium,osmium, iridium, and rhodium. Of this group, platinum and palladium areaccorded preference. Each of the platinum metals may occur in a varietyof compounds. Thus, suitable platinum compounds include chloroplatinicacid, platinous chloride and various compounds containing the platinumammine complex. The compounds of the use ful platinum metals may besubdivided into compounds in which the metal is present in the cation ofthe compound and compounds in which it is present in the anion of thecompound. Both types of compounds, that is types which contain the metalas the cationic state and those which contain the metal in the anionicstate may be used. It is, however, a preferred aspect of the method ofthe invention to employ ionizable platinum metal compounds in which themetal is in the cationic state, i.e. in the form of a cation or cationcomplex, since with such compounds exchange of the original metal ioncontained in the metal aluminosilicate crystalline zeolite with theplatinum metalcontaining cation is readily achieved. A solution in whichthe platinum metals are in the form of a cation or cationic complex,e.g. Pt(NH Cl is readily distinguishable from one in which they are inthe anionic portion, e.g. Na [PtCl by contacting such solutions with thesodium salt of an orangic cation exchanger. Under such conditions, thecation which contains platinum will be removed from solution by theexchanger, while the platinum metal-containing anion will besubstantially unaffected.

When employing a platinum metal compound in which the platinum metal isin the cationic form, it has been found that the platinummetal-containing cation undergoes exchange for the cation originallypresent in the crystalline aluminosilicate zeolite. Thus, using platinumammine chloride solution as the platinum metal solution and syntheticfaujasite (Molecular Sieve 13X) containing 13.0 weight percent sodium asthe crystalline zeolite, it was found that, at equilibrium, the solidafter water-Washing and drying, contained 4.4 weight percent sodium and16.4 weight percent platinum. These sodium and platinum analysesindicate that for every platinum atom added to the synthetic faujasite,3.87 sodium atoms were lost, and that the platinum ammine solutionconsisted essentially of tetravalent platinum-containing cations.

A further indication that the deposition of platinum by the use ofplatinum ammine chloride is an ion exchange process in thatwater-washing does not remove the platinum but salt washing does effectsuch removal. Thus, a synthetic faujasite (Molecular Sieve 13X) materialcontaining 0.90 weight percent platinum was washed with sodium chlorideand the platinum level was reduced to 0.03 weight percent.

It is contemplated that water will ordinarily be the solvent in theplatinum metal-containing solutions used. However, it will be understoodthat other solvents, although generally less preferred, may also beused. Thus, in addition to aqueous solutions, alcoholic solutions etc.of the platinum metal-containing compounds may be employed in thepresent process. The compounds of the platinum metals undergo ionizationin the particular solvent used. The concentration of the platinum metalcompound in the solution employed may vary widely depending on theamount of platinum metal desired in the final catalyst composition andon the conditions under which contact between the crystallinealuminosilicate zeolite and such solution is effected. Other conditionsbeing equal, a shorter time of contact between the crystalline zeoliteand platinum metal-containing solution may be used with the moreconcentrated solutions, while a longer period of contact is requiredwith the more dilute solutions.

The solutions of platinum metal compound may be contacted with thecrystalline zeolite of uniform pore structure in the form of either afine powder, a compressed pellet or an extruded pellet. When in the formof a pellet, the crystalline zeolite may be combined with a suitablebinder such as clay. The crystalline zeolite is a metal aluminosilicate,initially free of platinum metal having rigid three dimensional networkscharacterized by uniform interstitial dimensions sufficiently large topermit introduction by ion exchange of a platinum metal-containing ion.Generally, the uniform pore structure of the crystalline zeolite will bemade up of pores sufficiently large to at least admit cyclohexane andusually approximately 7 to 13 Angstroms in diameter. In particular, itis preferred to employ crystalline zeolites having pores approximately10 to 13 Angstroms in diameter since with the latter, exchange of theoriginal non-platinum metal of the aluminosilicate with platinum metalis readily realized. The metal originally contained in the crystallinealuminosilicate zeolite will generally be sodium or calcium, althoughthese may be replaced at least in part by other ions which do notordinarily affect the crystalline structure such as for example, silver,lithium, potassium, magnesium, cobalt and also ammonium ions.

When the solution contains the preferred cationic form of the platinummetal, such metal exchanges with the cation of the zeolite in the poresof the crystal structure. Because of the strong affinity of the zeolitesfor platinum metal cations, it has been observed that there is atendency for the platinum metals to deposit in large quantities at thefirst point of contact which results in an uneven distribution of theactive platinum metal on the zeolite. Moreover, excessively high levelsof platinum metal, either locally or throughout the catalyst particle,adversely affect the stability of the crystalline structure. It has beendiscovered, in one embodiment of the invention, that by including anexcess of a foreign salt such as a mineral acid salt of a non-platinummetal which does not adversely affect the crystalline structure of thezeolite, for example, sodium, potassium, lithium, zinc, cadmium,mercury, magnesium, calcium, cobalt, silver, or ammonium in the solutionof platinum metal compound and immersing the zeolite in such solution,the tendency for uneven distribution, as well as the content of platinummetal in the final composition may be very well controlled. The foreignsalt used may contain the same cation as the crystalline zeolite or ifit is desired to exchange the cation of the crystalline zeolite toachieve a desired selectivity of pore size, the foreign salt may be asalt of the new cation. While, a wide range of foreign salt may beincluded in the platinum metal compound solution, those of the mineralacids, i.e., hydrochloric,

sulfuric and nitric acids being comparatively inexpensive and readilyavailable are preferred. Salts which contain ions that destroy thecrystal diffraction properties of the zeolite are to be avoided. Suchundersirable ions include for example, those of barium, copper and iron.Thus, while it is a distinct advantage of this invention that theselectivity of the novel catalyst described herein may be modified bysimple control of the ionic form of the zeolite, the useful forms of thezeolite are those for which the crystal lattice structure remainssubstantially intact and which show X-ray diffraction patterns in whichspacings are characteristic of the crystalline aluminosilicate latticeirrespective of which cation is contained in the zeolite. The ratio offoreign salt to platinum metal compound in the solution used may varywidely depend ing on the particular crystalline zeolite employed, thechemical nature of the platinum metal compound used and the content ofplatinum metal desired in the finished catalyst. In general, a highratio of foreign salt to platinum metal compound produces a low platinummetal content in the final catalyst and conversely a low ratio offoreign salt to platinum metal compound produces a high platinum metalcontent in the final catalyst. As a rule, the ion ratio of platinummetal to non-platinum metal, derived from the foreign salt, isgenerally, between about l lO and about 1, to afford a resultingcomposite which contains 0.001 to 5 percent by weight platinum metal.

The volume of solution containing platinum metal compound and preferablyfurther containing a foreign salt as described above may be justsuificient to be adsorbed by the crystalline zeolite. Generally,however, an excess of solution is employed and such excess is removedfrom contact with the crystalline zeolite after a suitable period ofcontact and prior to drying of the zeolite. The time of contact betweenthe solution of platinum metal compound and crystalline zeolite is suchas to effect deposition on the crystalline structure of the platinummetal-containing ion derived from such solution. It will be appreciatedthat such period of contact may vary widely depending on the temperatureof the solution, the nature of crystalline zeolite used, the particularplatinum metal compound employed, and the concentration of platinummetal desired in the final catalyst. Thus, the time of contact mayextend from a very brief period of the order of minutes for smallparticles to long periods of the order of days for large pellets.Generally, the time of contact will, depending on the variousaforementioned factors, be within the range of 5 minutes to 10 days. Thetemperature of the solution will ordinarily be room temperature, but maybe an elevated temperature below the boiling point of the solution.

After the contact period the crystalline zeolite is removed from theplatinum metal compound solution. Excess platinum metal compound andforeign salt, if employed, are removed, suitably by washing with water.The resulting material is then dried, generally in air, to removesubstantially all of the water therefrom.

The dried material is then subjected to an activating treatmentessential to render the final composition catalytically active. Suchtreatment involves heating the dried material at a temperature in theapproximate range of 250 F. to 1100 F. to eifect at least partialconversion of the platinum metal-containing ion to a catalyticallyactive state. In a preferred aspect of the invention, the dried materialis subjected to treatment in an atmosphere containing free oxygen, suchas air, at a temperature within the approximate range of 250 F. to 1100F. for hour to 24 hours and thereafter in an atmosphere of hydrogen at atemperature within the above range to effect at least partial reductionof the platinum metalcontaining ion to platinum metal.

The advantage of utilizing an activating treatment employing initiallyan atmosphere containing free oxygen and thereafter an atmosphere ofhydrogen as compared to hydrogen alone is shown by the following data inwhich synthetic faujasite (Molecular Sieve 13X) was contacted withplatinic ammine chloride in an amount such that the finished catalystcontained 0.82 weight percent 6.0 and was slightly cloudy due to areaction product of chloroplatinic acid and ammonium hydroxide. Thesolution was filtered and the resulting colorless filtrate was found tocontain 1.66 weight percent of platinum. Platinum in such solution wasin the form of platinic ammine platinum. A portion of the solid washeated while initialchloride, i.e. in the cationic form.

ly air and later hydrogen was passed over it. A second Seven millilitersof the above platinic ammine chloride portion of the solid was heatedonly in the presence of solution were contacted with 5.68 grams ofMolecular flowing hydrogen. The results are set forth below: Sieve A(calcium aluminosilicate) in pellet form for a Gas Temp, F. Time GasTemp, F. Time Gas TenIip, Time DA* Nitrogen 75 2honrs. H2 Rising to800.. 4days. H2 800 1%hrs 22 Dry Air Rising to 800-. Bdays. Air 8002l1rs. I12 800 Zhrs 1,000

*DA is dehydrogenation activity, measured by passing cyelohexane andhydrogen at atmospheric pressure over a thin layer of the catalyst at arate of 55.2 cc. of liquid cyclohexaue per hour and hydrogen in a molarratio of 4:1 of hydrogen to hydrocarbon at 806 F. The rate of benzeneproduction, expressed as moles benzene l0- per second per grain ofcatalyst is reported as the dehygenation activity or DA.

It will be seen from the foregoing results referring to dehydrogenationactivity of the respective catalysts that there is a marked advantage inthe use of a gas containing free oxygen, i.e. air, as compared tohydrogen in the preliminary portion of the activation procedure.

The catalyst of this invention contains platinum metal deposited on thecrystalline aluminosilicate zeolite. When the platinum metal compoundused contains platinum metal in the cationic state, and particularlywhen an additional foreign salt as described hereinabove is present inthe solution of such platinum metal compound, uniform distribution ofplatinum metal is achieved throughout the zeolitic crystallinestructure. The concentration of platinum metal in the finished catalystmay vary depending on the use for which such catalyst is intended. Thecontent of platinum metal in the finished catalyst generally, however,is within the approximate range of 0.001 to 5 percent by weight.

The platinum metal-containing catalysts described herein exhibit highactivity for selected members of a hydrocarbon class. Such selectivehigh activity appears to be restricted to those molecules which do notexceed a maximum critical diameter, corresponding to the particular poresize of the crystalline zeolite. It appears that the major portion ofthe deposited platinum metal is situated within the crystals of thezeolite, and that the crystals of the zeolite admit or reject a reactantmolecule depending on whether or not the diameter of the moleculeexceeds the size of the opening in the crystal face. Thus, it appearsthat a molecule which cannot enter the crystal cannot undergo anysubstantial reaction. There are numerous applications for the catalystsof the present invention. For example, with a mixture of benzene andtriethylbenzene, the benzene component undergoes selective hydrogenationupon contacting such mixture, under hydrogenation conditions with acatalyst having a molecular sieve structure of the X series, i.e.Molecular Sieve X or Molecular Sieve 13X upon which has been dispersed aplatinum metal. In such a reaction, the benzene molecules aresufliciently small in size to enter the pores of the molecular sievestructure while triethylbenzene is sufiiciently large to be excludedfrom the interior of the crystalline pore structure. Accordingly, thebenzene reactant readily comes into contact with the platinummetal-bearing surfaces while the triethylbenzene reactant issubstantially excluded from such contact and accordingly undergoesnegligible hydrogenation.

The following examples will serve to illustrate the catalyst and methodof this invention without limiting the same:

Example 1 Fifty milliliters of chloroplatinic acid solution containing2.0 grams of platinum were mixed with 1240 milliliters of ammoniumhydroxide solution containing 28 percent by weight NH The mixture washeated until the volume was 110 milliliters. The pH of such solution wasperiod of approximately 20 days. At the end of this time, excesssolution was drained from the pellets. The pellets were then heated inair at 230 F. for one hour and thereafter at 800 F. for 1% hours. Thepellets were then flushed with nitrogen, heated for 2 hours in anatmosphere of hydrogen at 800 F., flushed with nitrogen and finallycooled. The finished pellets contained 0.63 weight percent platinum.

The product pellets were powdered to particles which passed through amesh (Tyler) screen and employed as a catalyst in the liquid phasehydrogenation of henzene. For such reaction, 0.829 gram of catalystpowder was mixed with 25 milliliters of benzene. The reaction took placein a closed vessel which was shaken mechanically. Hydrogen was added tothe system until the total pressure was about 30 pounds per square inchgauge. The reaction temperature was F. Under such conditions, benzenewas converted to cyclohexane. The rate of conversion was determined bymeasuring the rate of pressure drop due to hydrogen consumption. It wasfound that 3.82 10 moles of liquid benzene were converted per hour pergram of catalyst.

Example 2 In this example, a platinum-containing catalyst was preparedby utilizing a crystalline calcium aluminosilicate having channels ofabout 10 Angstroms in diameter, i.e. Molecular Sieve 10X andchloroplatinic acid in which platinum is in the anionic form.

Twenty-five milliliters of a solution of chloroplatinic acid containing0.0625 gram of platinum was mixed with 17.4 grams of Molecular Sieve 10Xin the form of clay bonded pellets (containing about 20 percent byweight clay) and permitted to stand for 1 day. The excess solution wasthen drained from the pellets which were thereafter heated for 1 hour inair at 230 F. and activated by heating for 2 hours at 800 F. The productcontained 0.14 Weight percent platinum.

The product pellets were powdered to particles which passed through a100 mesh (Tyler) screen and employed as a catalyst in the hydrogenationof benzene. For such reaction, 2.81 grams of catalyst powder were mixedwith 50 milliliters of benzene under the conditions of Example 1. It wasfound that 1.26 10 moles of liquid benzene were converted per hour pergram of catalyst.

Example 3 In this example, a platinum-containing catalyst was preparedby utilizing a crystalline sodium aluminosilicate having channels about13 Angstroms in diameter, i.e. Molecular Sieve 13X and platinous amminechloride in which platinum is in the cationic form.

Ten and six tenths (10.6) grams of chloroplatinic acid [H PtCl -6H O]were dissolved in 50 milliliters of water. 1.07 grams of solid hydrazinedihydrochloride were added in small portions to effect reduction. Thesolution was kept on a steam bath until the liquid volume diminished to5 milliliters, and was thereafter heated for a day at 230 F. in air,followed by 4 hours heating in air at 300 F. The resulting solidproduct, platinous chloride (PtCl was freed of impurities by waterwashing.

The purified platinous chloride was dissolved in 400 milliliters ofconcentrated ammonium hydroxide, containing 28 weight percent NH byboiling with frequent ammonium hydroxide additions for 7 hours, andthereafter for 2 additional hours without further ammonium hydroxideaddition. The final volume of the resulting solution of platinous amminechloride was 200 milliliters.

Fifty milliliters of the filtered platinous ammine chloride solutionwere contacted with 3.25 grams of Molecular Sieve 13X in pellet form forapproximately 14 days. At the end of this time, excess solution wasdrained from the pellets. The pellets were then heated in air for 1%hours at 230 F. and thereafter at 800 F. for 2 hours. The pellets werethen flushed with nitrogen, heated for 2 hours in an atmosphere ofhydrogen at 800 F. and finally flushed with nitrogen. The finishedpellets contained 7.74 weight percent platinum.

The product pellets were powdered to particles which passed through a100 mesh (Tyler) screen and employed as a catalyst in thedehydrogenation of cyclohexane in the DA test described hereinabove. Theactivity of the catalyst on the DA scale was 241 compared with adehydrogenation activity (DA) for the untreated 13X material ofessentially zero.

Example 4 In this example, a palladium-containing catalyst was preparedby utilizing a crystalline sodium aluminosilicate having channels ofabout 13 Angstroms in diameter, i.e. Molecular Sieve 13X and palladousammine chloride, in which palladium was in the cationic form.

Fifty-eight hundredths (0.58) of a gram of palladium chloride [PdCl'2I-I was mixed with 47.4 milliliters of water and 15.8 milliliters ofammonium hydroxide, containing 28 weight percent NH and permitted tostand for 16 hours.

Six milliliters of the resulting palladous ammine chloride werecontacted with 2.9 grams of Molecular Sieve 13X for 15 days. At the endof this time, excess solution was drained from the solid, which washeated in air for 1 hour at 230 F. and thereafter at 800 F. for 1 /2hours. The solid was then flushed with nitrogen, heated for 2 hours inhydrogen at 800 F. and finally flushed with nitrogen. The finishedcatalyst contained 1.3 weight percent palladium.

The solid product was powdered to particles which passed through a 100mesh (Tyler) screen and employed as a catalyst in the dehydrogenation ofcyclohexane in the DA test described hereinabove. The activity of thecatalyst on the DA scale was 67 as compared with a dehydrogenationactivity (DA) for the untreated 13X material of essentially zero.

Example 5 In this example, a platinum-containing catalyst was preparedby utilizing a crystalline sodium aluminosilicate having channels about13 Angstroms in diameter, i.e. Molecular Sieve 13X and hydrolyzedchloroplatinic acid.

To 123 milliliters of an aqueous solution containing 9.38 gramschloroplatinic acid [H PtCl 6H O] was added 27 milliliters of 7.5 molaraqueous solution of sodium hydroxide. The mixture was boiled for /2hour. When cooled, the pH of the mixture was 11.25. The solution wasneutralized with 13.2 milliliters of glacial acetic acid, to give a pHof 7.10. Solid material in the mixture was filtered off.

Seventy-five milliliters of the resulting clear solution was contactedwith 1.06 grams of Molecular Sieve 13X for 14 days. Excess solution wasthen drained from the solid. Dry air was passed over the solid for 16hours at room temperature, at 140 F. for 7 hours, at 210 F. for

12 18 hours, at 345 F. for 6 hours, at 625 F. for 2 hours and at 800 F.for 2 hours. The solid was then flushed with nitrogen, treated withhydrogen for 2 hours at 800 F. and finally flushed with nitrogen. Thefinished product contained 5.78 weight percent platinum.

The solid product was powdered to particles which passed through a mesh(Tyler) screen and employed as a catalyst in the dehydrogenation ofcyclohexane in the DA test. The activity of this catalyst on the DAscale was 706 showing it to be an exceptionally active catalyst.

Example 6 In this example, a platinum-containing catalyst was preparedby utilizing a crystalline sodium aluminosilicate having channels ofabout 13 Angstrom units in diameter, i.e. Molecular Sieve 13X, platinicammine chloride and sodium chloride.

One hundred grams of Molecular Sieve 13X pellets (containing 20 percentclay as a bonding agent) were contacted with 2550 milliliters of asolution containing sodium chloride and platinum as platinic amminechloride. To make such solution, 50 milliliters of the platinic amminechloride solution of Example 1 Was added to 2500 milliliters of a 3.50molar sodium chloride solution. After approximately 13 days contact,excess solution was drained from the solid and the solid was washed withwater until free of chloride ion. The solid was dried and calcined inair for 6 hours at a gradually increasing temperature to 800 F. Thesolid was then flushed with nitrogen, treated for 2 hours at 800 F. inan atmosphere of hydrogen and finally flushed with nitrogen. Thefinished prod not contained 0.65 weight percent of uniformly distributedplatinum.

The product was employed as a catalyst in liquid phase hydrogenation ofboth benzene and triethylbenzene. For the hydrogenation of benzene, 5grams of the catalyst was mixed with 10 milliliters of benzene.Operation took place at a temperature of F. and a hydrogen pressure of30 pounds per square inch gauge. The moles of liquid benzeneXl0-converted per hour per gram of catalyst was 4.84, as compared with aconversion of benzene of less than 0.1 mole for the untreated 13Xmaterial. For the hydrogenation of triethylbenzene, 5 grams of thecatalyst was mixed with 10 milliliters of triethylbenzene. Reaction tookplace at a temperature of 145 F. and a hydrogen pressure of 30 poundsper square inch gauge. The moles of liquid triethylbcnZeneX 103converted per hour per gram of catalyst was 0.97. The rate ofhydrogenating the bulky triethylbenzene molecule was accordingly only 20percent of the benzene hydrogenation rate, illustrating selectivehydrogenation of the smaller benzene molecule as compared with thelarger molecule of triethylbenzene. In contrast to the selectivehydrogenation observed with the present catalyst, utilization of aconventional hydrogenating catalyst of 6 to 8 mesh (Tyler) particlescontaining 1.02 weight percent platinum deposited on a silica gelsupport showed under the foregoing conditions of hydrogenationsubstantial equal rates of conversion for the benzene andtriethylbenzene reactants. With such conventional catalyst, 2l.4 10moles of liquid benzene and 17.4 10" moles of liquid triethylbenzenewere converted per hour per gram of catalyst. Thus, the catalyst of theinvention exhibits a much greater selectivity in hydrogenation ofbenzene as compared with triethylbenzene than does a conventionalcatalyst of platinum on silica gel.

Example 7 In this example, a platinum-containing catalyst was preparedby utilizing a crystalline calcium aluminosilicate having channels ofabout 10 Angstrom units in diameter, i.e. Molecular Sieve 10X, p-latinicammine chloride and calcium chloride.

One hundred grams of Molecular Sieve l10X in the form of pelletscontaining 20 percent clay as a bonding agent were contacted with 2040milliliters of a solution containing calcium chloride and platinum asplatinic ammine chloride. Such solution was made by mixing 40milliliters of the platinic ammine solution of Example 1 with 2000milliliters of a 5.69 molar calcium chloride solution. Afterapproximately 13 days contact, excess solution was drained from thesolid and the solid was washed with water until free of chloride ion.The solid was dried and calcined as in Example 6. The finished productcontained 0.24 weight percent of uniformly distributed platmum.

The product was employed as a catalyst in liquid phase hydrogenation ofboth benzene and triethylbenzene under the conditions described inExample 6. The moles of liquid benzene converted was 4.0? land the molesof liquid triethylbenzene was only 0.18 1O- per hour per gram of thiscatalyst. The rate of hydrogenating the bulky triethylbenzene moleculewas accordingly only 4 percent of the benzene hydrogenation rate,showing an even greater selectivity than that of the catalyst of Example6.

Example 8 This example illustrates the necessity for the thermalactivation treatment in the preparation of the platinum metal catalystsdescribed herein.

Twenty grams of hydrated chloroplatinic acid (40% Pt) was dissolved in200 ml. water. To this solution 4800 ml. concentrated NH OH was added.After standing 16 hours, the solution was boiled down to 400 ml. Thesolution was then mixed with 10 liters of 1.5 molar calcium chloride.

Four hundred grams of a crystalline calcium aluminosilicate havingchannels of about 10 Angstrom units in diameter, i.e. Molecular Sieve10X, was added to the solution and allowed to stand for several days.The solid was then filtered off and rinsed until the rinse was free ofchloride ion (AgNO test). The solid was then dried in an air oven at amaximum temperature of 230 F. For easier manipulation, the fine powderwas pelleted and ground to a coarse powder.

The unactivated solid was evaluated for hydrogenation activity byplacing 0.2 gram in a Pyrex tube, passing over the powder 25 mL/min. ofbutene-l mixed with an equal volume of hydrogen at ambient temperature,and analyzing the resulting products in a vapor fractometer. To evaluateactivation procedures, samples were treated as indicated in thefollowing table, brought back to room temperature and evaluated asdescribed above. The results are summarized below:

It was noted that the inactive materials of tests l3 inclusive werewhite while those of tests 4-5 were a very light grey after activation.

It will be seen from the above example that a thermal activationtreatment is essential in converting the platinum metal to acatalytically active state. In this example, butene-l was readilyhydrogenated at ambient temperature in the presence of catalysts thatwere activated by simple heat-treament under nitrogen but was unaffectedby the untreated platinum catalyst.

It is to be understood that the above description is merely illustrativeof preferred embodiments of this invention, of which many variations maybe made by those skilled in the art without departing from the spiritthereof.

We claim:

1. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline aluminosilicate zeolite initiallyfree of platinum metal and having rigid three dimensional networkscharacterized by uniform interstitial dimensions, sufficiently large topermit introduction by ion exchange of a platinum metal-containing ion,with a solution of an ionizable platinum metal compound and an ionizablenon-platinum metal mineral acid salt for a suflicient period of time toeffect uniform distribution on the crystalline zeolite of a platinummetal-containing ion derived from said solution, drying the resultingcomposite and activating the same by thermally treating at a temperaturein the approximate range of 250 F. to 1100 F. to effect at least partialconversion of said platinum metal-containing ion to a catalyticallyactive state.

2. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline nonplatinum metal aluminosilicatezeolite having rigid three dimensional networks characterized by uniforminterstitial dimensions, sufficiently large to permit introduction byion exchange of a platinum metal-containing ion, with a solution of anionizable platinum metal compound and an ionizable non-platinum metalmineral acid salt for a sufiicient period of time to effect uniformdistribution on the crystalline structure of said zeolite of a platinummetal-containing ion derived from said solution, drying the resultingcomposite and activating the same by treating in an atmospherecontaining free oxygen at a temperature within the approximate range of250 F. to 1100 F. for about A hour to about 24 hours and thereafter inan atmosphere of hydrogen at a temperature within the aforementionedrange to effect at least partial reduction of said platinummetal-containing ion to platinum metal.

3. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline zeolite consisting essentially of ametal aluminosilicate, which metal is selected from the group consistingof sodium and calcium and having a structure of rigid three dimensionalnetworks characterized by uniform pores approximately 7 to 13 Angstromsin diameter with a solution of an ionizable platinum metal compound anda mineral acid salt of a metal selected from the group consisting ofsodium and calcium for a sufficient period of time to effect uniformdistribution on the crystalline zeolite of a platinum metal-containingion derived from said solution, drying the resulting composite andactivating the same by thermally treating at a temperature in theapproximate range of 250 F. to 1100 F. to effect at least partialconversion of said platinum metal-containing ion to a catalyticallyactive state.

4. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline zeolite consisting essentially of ametal aluminosilicate, which metal is selected from the group consistingof sodium and calcium and having a structure of rigid three dimensionalnetworks characterized by uniform pores approximately 7 to 13 Angstromsin diameter with a solution of an ionizable platinum metal compound inwhich the platinum metal is in the cationic state and a mineral acidsalt of a metal selected from the group consisting of sodium and calciumfor a suflicient period of time to effect substantial exchange of themetal ion initially contained in said metal aluminosilicate withplatinum metal-containing cation, drying the resulting composite andactivating the same by thermally treating at a temperature in theapproximate range of 250 F. to 1100 F. to effect at least partialconversion of said platinum metal-containing cation to a catalyticallyactive state.

5. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline aluminosilicate zeolite initiallyfree of platinum metal and having rigid three dimensional networkscharacterized by uniform interstitial dimensions, sufficiently large topermit introduction by ion exchange of a platinum metalcontaining ion,with a solution of an ionizable platinum metal compound and an ionizablenon-platinum metal mineral acid salt, the ion ratio of platinum metal tonon-platinum metal contained in said solution being between about 1 10-and about 1, for a sufficient period of time to effect uniformdistribution on the crystalline zeolite of a platinum metal-containingion, drying the resulting composite and activating the same by thermallytreating at a temperature in the approximate range of 250 F. to 1100 F.to effect at least partial conversion of said platinum metal-containingion to a catalytically active state.

6 A method for preparing a platinum-containing catalyst which comprisescontacting a crystalline zeolite consisting essentially of a metalaluminosilicate, which metal is selected from the group consisting ofsodium and calcium and having a structure of rigid three dimensionalnetworks characterized by uniform pores approximately 7 to 13 Angstromsin diameter with a solution of an ionizable platinum compound in whichplatinum is in the cationic state and a mineral acid salt of a metalselected from the group consisting of sodium and calcium, the ion ratioof platinum to metal derived from said mineral acid salt being betweenabout 1 10 and about 1, for a sutlicient period of time to effectuniform distribution on the metal aluminosilicate of platinumcontainingion, drying the resulting composite and activating the same by thermallytreating at a temperature in the approximate range of 250 F. to 1100 F.to effect at least partial conversion of said platinum-containing ion toa catalytically active state.

7. A method for preparing a palladium-containing catalyst whichcomprises contacting a crystalline zeolite consisting essentially of ametal aluminosilicate, which metal is selected from the group consistingof sodium and calcium and having a structure of rigid three dimensionalnetworks characterized by uniform pores approximately 7 to 13 Angstromsin diameter with a solution of an ionizable palladium compound in whichpalladium is in the cationic state and a mineral acid salt of a metalselected from the group consisting of sodium and calcium, the ion ratioof palladium to metal derived from said mineral acid salt being betweenabout 1 10 and about 1, for a sufficient period of time to effectuniform distribution on the metal aluminosilicate of palladiumcontainingion, drying the resulting composite and activating the same by thermallytreating at a temperature in the approximate range of 250 F. to 1100 F.to effect at least partial conversion of said palladium-containing ionto a catalytically active state.

8. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline aluminosilicate zeolite initiallyfree of platinum metal and having rigid three-dimensional networkscharacterized by uniform interstitial dimensions, sufiiciently large topermit introduction by ion exchange of a platinum metal-containing ion,with a solution of an ionizable platinum metal compound, and anionizable mineral acid salt of a metal selected from the groupconsisting of sodium, potassium, lithium, zinc, cadmium, mercury,magnesium, calcium, cobalt, silver and ammonium for a sufiicient periodof time to effect uniform distribution on the crystalline zeolite of aplatinum metal-containing ion derived from said solution, drying theresulting composite and activating the same by thermally treating at atemperature in the approximate range of 250 F. to 1100 F. to effect atleast partial conversion of said platinum metal-containing ion to acatalytically active state.

9. A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline aluminosilicate zeolite initiallyfree of platinum metal, and having rigid three-dimensional networkscharacterized by uniform interstitial dimensions, sufiiciently large topermit introduction by ion exchange of a platinum metal-containing ion,with a solution of an ionizable platinum metal compound and an ionizablemineral acid salt having the same cation as said aluminosilicate zeolitefor a sufiicient period of time to effect uniform distribution on thecrystalline zeolite of a platinum metal-containing ion derived from saidsolution, drying the resulting composite and activating the same bythermally treating at a temperature in the approximate range of 250 F.to 1100 F. to effect at least partial conversion of said platinummetal-containing ion to a catalytically active state.

if). A method for preparing a platinum metal-containing catalyst whichcomprises contacting a crystalline aluminosilicate zeolite initiallyfree of platinum metal, and having rigid three-dimensional networkscharacterized by uniform interstitial dimensions, sufficiently large topermit introduction by ion exchange of a platinum metal-containing ion,with a solution of an ionizable platinum metal compound, and a mineralacid salt of a metal selected from the group consisting of sodium andcalcium for a sufiicient period of time to effect uniform distributionon the crystalline zeolite of a platinum metalcontaining ion derivedfrom said solution, drying the resulting composite and activating theame by thermally treating at a temperature in the approximate range of250 F. to 1000 F. to efifect at least partial conversion of saidplatinum metal-containing ion to a catalytically active state.

References Cited by the Examiner UNITED STATES PATENTS 1,840,450 1/1932Jaeger 252-454 2,306,610 12/1942 Barrer 252-449 2,413,134 12/1946 Barrer252-449 2,882,243 4/1959 Milton 252-455 2,898,387 8/1959 Teter 252-466MAURICE A. BRINDISI, Primary Examiner.

JULIUS GREENWALD, Examiner.

1. A METHOD FOR PREPARING A PLATINUM METAL-CONTAINING CATALYST WHICHCOMPRISES CONTACTING A CRYSTALLINE ALUMINOSILICATE ZEOLITE INITIALLYFREE OF PLANTIUM METAL AND HAVING RIGID THREE DIMENSIONAL NETWORKSCHARACTERIZED BY UNIFORM INTERSTITIAL DIMENSIONS, SUFFICIENTLY LARGE TOPERMIT INTRODUCTION BY ION EXCHANGE OF A PLATINUM METAL-CONTAINING ION,WITH A SOLUTION OF AN IONIZABLE PLATINUM METAL COMPOUND AND AN IONIZABLENON-PLATINUM METAL MINERAL ACID SALT FOR A SUFFICIENT PERIOD OF TIME TOEFFECT UNIFORM DISTRIBUTION ON THE CRYSTALLINE ZEOLITE OF A PLATINUMMETAL-CONTAINING ION DERIVED FROM SAID SOLUTION, DRYING THE RESULTINGCOMPOSITE AND ACTIVATING THE SAME BY THERMALLY TREATING AT A TEMPERATUREIN THE APPROXIMATE RANGE OF 250*F. TO 1100*F. TO EFFECT AT LEAST PARTIALCONVERSION OF SAID PLATINUM METAL-CONTAINING ION TO A CATALYTICALLYACTIVE STATE.